Fetlock

Fetlock is the common name in horses, large animals, and sometimes dogs for the metacarpophalangeal and metatarsophalangeal joints (MCPJ and MTPJ).

[1] "Feather" refers to the particularly long, luxuriant hair growth over the lower leg and fetlock that is characteristic of certain breeds.

While the fetlock is sometimes colloquially referred to as an "ankle", even by horse experts, that terminology is misleading.

The fetlock is a metacarpo- or metatarsophalangeal joint which corresponds to the human upper knuckle, such as that on the ball of the foot.

This usage likely originated from early definitions of "ankle" as "between foot and leg" derived from the common root of "angle" meaning to bend.